From the AppleInsider’s Daniel Eran Dilger:
“Readers report that Apple’s tech support forums originally confirmed that a iOS 4.0.1 software fix addressing the issue would ship early next week (as early as Monday), before the comments were subsequently taken down along with all the other related discussion about the matter.
The fix is expected to address a issue in iOS 4 related to radio frequency calibration of the baseband. Readers who saw the original forum discussions say that the issue is believed to occur when switching frequencies; because the lag is allegedly not calibrated correctly, it results in the device reporting “no service” rather than switching to the frequency with the best signal to noise ratio.
iOS 4 introduced some enhancements to how the baseband selects which frequencies to use, so it makes sense that the error may have crept into those changes. Additionally, this explains why iOS 4 has also caused similar problems for iPhone 3GS users.
Additional readers have shared other related experiences that also corroborate the idea that the issue is related to iOS 4′s software control of the baseband, including the fact that the issue seems easily reproducible when connecting to a WWAN 3G network but does not appear when connecting to a Microcell 3G. If the problem were simply hardware related issues of the antenna design, it should only affect iPhone 4 units with that new design and should occur at all times, regardless of the tower type. That is not being observed.
The core software problem is likely augmented by hand placement, as Jobs noted in pointing out that holding the new phone (or any mobile device) in such a way that attenuates the signal should simply be avoided.”